Anterior Chamber Depth and the Long-Term Safety of Implantable Collamer Lens Surgery: A Case for Re-Evaluating Age-Stratified Indication Criteria.

Purpose: Implantable Collamer Lens (ICL) surgery is mostly performed in patients aged 20-40, with current minimum anterior chamber depth (ACD) eligibility of approximately 2.8-3.0 mm. A shallow chamber carries two distinct long-term risks: corneal endothelial cell loss, determined principally by the endothelium-to-implant distance, and angle closure, determined by progressive anterior segment crowding. This static criterion accounts for neither of the two dynamic factors that reduce effective ACD over decades: age-related crystalline lens thickening, and vault-related anterior displacement of the implant. We propose age-stratified ACD values, anchored to the empirical 2.4 mm threshold for primary angle closure in East Asians, as risk-stratification factors. Methods: We conducted a structured narrative review of ACD and primary angle-closure disease in East Asians including Japanese data; age-related anterior segment biometry; vault dynamics; and long-term ICL outcomes, integrated into a quantitative model presented as a conservative estimate rather than a definitive predictor. Results: The 2.4 mm threshold is confirmed in East Asian populations and consistent with Japanese population-based biometry. ACD shallows at approximately 0.011-0.012 mm/year; vault contributes a further functional reduction of approximately 0.25-0.40 mm. A patient implanted at age 20 with an initial ACD of 2.8 mm may approach 2.0 mm by age 60. Age-stratified minimum values of 3.2, 3.1 and 3.0 mm for the third, fourth and fifth decades preserve a margin above 2.4 mm; sensitivity analysis across lens-extraction ages of 45-60 years yields 3.0-3.2 mm. Independently, ten-year data in eyes with ACD below 2.8 mm show endothelial loss at approximately twice the physiological rate. Conclusion: Current criteria reflect the eye's status at a single time point. We suggest age-stratified ACD values be used as risk-stratification factors alongside gonioscopy and anterior segment imaging, not as standalone exclusion criteria, in parallel with established corneal refractive surgery criteria. Long-term validation is warranted.